On January 27, Rowan Laxton, a senior British diplomat who is the deputy head of the Foreign and Commonwealth Office's South Asia group, was watching the news from Gaza, while exercising in his gym. In the words of the Daily Mail, the diplomat is reported to have "launched a foul-mouthed antisemitic tirade" during the course of which he cursed the "fucking Jews". Laxton is reported to have refused to quieten down when approached by fellow gym users. He was ultimately arrested by the police for a public order offence.

The day that Rowan Laxton was arrested was Holocaust Memorial Day. This country's largest anti-racist organisation, Unite Against Fascism commemorated that event by encouraging people to light candles. It had nothing to say, in the following weeks, about the "fucking Jews" allegation against Laxton. Neither was the story reported in the Guardian, on the BBC website, or the Independent; although the centre-right Telegraph and Times had it.

I have to admit, I was initially slightly surprised to see how little concern on the antiracist left the spectacle of a senior British diplomat, arrested for a "fucking Jews" rant, had engendered. While it is important to note that Laxton denies making any antisemitic remark, it isn't as if antiracist organisations normally shy away from responding to complaints about public servants. For example, on the day following the publication of the story, Unite Against Fascism managed to organise a rally against a teacher who was a British National party member. But then, I shouldn't have been surprised. The last couple of months has seen the worst year on record for antisemitic incidents in the United Kingdom. Yet Unite Against Fascism has had nothing to say about that, either.

The problem, I think, is this. Although opposition to racism is now an article of faith for all mainstream political parties, the left has been the driving force in those organisations that set the antiracist agenda. There is a part of the left that is very comfortable condemning historical racism against Jews, at the hands of Nazis, back in the 1940s. It is, however, ambivalent when it comes to contemporary antisemitism: particularly when it can be "contextualised" within the Israel/Palestine conflict.

Frankly, the part of the left that runs Unite Against Fascism is not up to fighting contemporary antisemitism. Its joint secretaryship is shared by a member of the central committee of the Socialist Workers party, and by a member of the National Assembly Against Racism (NAAR), which is strongly supported by Socialist Action. Both these political groups have a history of overlooking antisemitism.

For years, the Socialist Workers party promoted and toured the self-described "ex-Jew" Gilad Atzmon. When SWP supporter and Childrens' Laureate Michael Rosen criticised the party for giving a platform to a performer who, he argued, voiced racist and antisemitic ideas, he was slapped down by central committee member Lindsey German and others. Socialist Action activists led the charge, with Ken Livingstone, to defend the Muslim Brotherhood Sheikh Yusuf al-Qaradawi, after the human rights campaigner Peter Tatchell had outed him as an inciter of terrorism, antisemitism and homophobia.

In January 2009, Qaradawi gave a sermon televised by Al-Jazeera in which, as the Times reported, he expressed the hope that the "believers" would one day inflict upon the Jews a "divine punishment", akin to Hitler's Holocaust. According to the Muslim Council of Britain, Qaradawi is a "renowned Islamic scholar" who "enjoys unparalleled respect and influence throughout the Muslim world". Although the chairman of a House of Commons select committee has protested about Qaradawi's remarks, I am not aware of any UK antiracist organisation having condemned them. Indeed, I have found no occasion on which Unite Against Fascism has spoken out against the genocidal antisemitism that is prevalent in Islamist political rhetoric. Apparently, they just don't see it as a problem.

The bottom line is this. Neither Socialist Action nor the Socialist Workers party will oppose racism against Jews, and other forms of bigotry, if they find it politically inconvenient to do so. Indeed, in 2006 and 2008, the Unite Against Fascism national conference featured Dr Daud Abdullah, the assistant secretary general Muslim Council of Britain. Yet Abdullah was the prime mover behind the MCB's disgraceful boycott of Holocaust Memorial Day. You might remember that the MCB's original justification for the boycott was that Holocaust Memorial Day "includes the controversial question of alleged Armenian genocide as well as the so-called gay genocide". This year, the MCB was back to boycotting Holocaust Memorial Day. Nevertheless, this did not disqualify its secretary general, Muhammad Abdul Bari, from being invited as a guest of honour to Unite Against Fascism's national conference in 2009.

Unite Against Fascism's weakness on antisemitism is both shocking and shameful. This is not, unfortunately, a story about goings-on in two marginal far left cults. Unite Against Fascism is the leading campaign against racism in the United Kingdom. It is supported by parliamentarians from all the major political parties, and by every significant trade union. It is Unite Against Fascism that sets the tone of the debate when it comes to opposing racism. They call the demonstrations and organise the conferences. It is to Unite Against Fascism that the national press turns, when racism rears its head.

Yet, the best that Unite Against Fascism can do, in these dark times, is to mumble about how awful the Holocaust was. What this means is that there is no broad-based campaign in this country to defend Jews from contemporary antisemitism.

This state of affairs is, quite frankly, terrifying. As others are warning here, there is every reason to believe that the defining themes of the present economic downturn will be xenophobic, anti-immigrant and racist politics. As conspiracy theories depicting Jews as controllers of the financial markets proliferate, antisemitism will undoubtedly also be part of that mix. Support for fascist parties tends to grow during crises, and we need a strong defence against that politics, with solidarity between and support from all parts of British society. However, with its sectarianism, silence on antisemitism and blindness to Islamist Jew-hatred, Unite Against Fascism just isn't up to the job.

We badly need a new campaign against racism and fascism, run properly by those at the political centre. The first step towards remedying this situation, is for the political mainstream to reclaim antiracist politics from the extreme left.